Mobile communications networks may be connected with the aid of GPRS (General Packet Radio System) or UMTS (Universal Mobile Telecommunications System) as packet-switching systems to further standard data networks which are based on the packet-switching principle, so-called packet data networks, such as the Internet. Data is in this case transported by a packet data network, for example the Internet, via a GPRS or UMTS network to a mobile communication unit (MS) using a number of standardized protocols, such as IP (Internet Protocol). The general configuration of a GPRS mobile radio network including in particular serving GPRS support nodes (SGSN) and gateway GPRS support nodes (GGSN) is known from the specialist journal “Funkschau” [Radio Show], 20/99, “IP im Mobilfunk” [IP in mobile radio]. Data coming from a public packet-switching network is transmitted by means of point-to-point connections or services (PtP services) via a GGSN to an SGSN, and from there to a mobile communication unit. In a system such as this, an SGSN has monitoring functions (relating, for example, to user mobility, user authorization, transport service monitoring, service access monitoring) and packet transport functions (such as the conversion of data between the transport tunnels to the GGSN or to the radio network). A GGSN controls the connection between a GPRS network and a packet-data-oriented external landline network, for example the Internet. A GGSN furthermore converts data packets between an external packet-switching landline network and a transport tunnel between a GGSN and SGSN.
UMTS and GSM/GPRS provide an IP multicast service which allows mobile users to receive multicast data. This multicast service is based on point-to-point connections (PtP) between a mobile communication unit (MS) and the GGSN. The multicast data comes, for example, from the mobile communications network or from a packet-oriented external landline network, for example the Internet, by means of a multicast server, for example. This multicast service does not, however, ensure efficient use of the resources available. A separate connection as far as the multicast function of the GGSN for the respective MC-IP address is set up, and the multicast service is thus produced, via point-to-point connections for each mobile communication unit (MS) which wishes to use a specific multicast service.